The invention relates to a device for the monitoring and regulation of material concentrations in chemical process, said substances reacting to completion in an exothermal reaction with othe substances, by measuring the temperature rise in this reaction. The apparatus comprises a measuring cell with supply lines for the reaction medium and the reacting substance, a discharge line, and temperature sensors. The apparatus serves in particular for determining and monitoring hydrogen peroxide and chlorite concentrations in scrubbing solutions for scrubbing the flue gases of, for example, waste-incineration plants or large capacity firing systems.
In many continuous and discontinuous chemical processes which operate with such substances as hydrogen peroxide, sodium chlorite or other oxidizing and reducing agents, it is necessary to monitor the concentration of these substances by continuously measuring and, if necessary, adjusting the amounts and concentration. This is also particularly true for modern processes of flue gas scrubbing, in which there are removed from the flue gases substances such as sulfur dioxide by means of solutions containing hydrogen peroxide, or nitrogen oxides by means of solutions containing sodium chlorite.
Aqueous sodium chlorite solutions have recently been used to convert the nitrogen monoxide contained in the flue gases of waste incineration plants to nitrogen dioxide by wet scrubbing. In acidic chlorite solutions, more or less free chlorine dioxide, which is extremely explosive, is formed depending on the pH. Thus, it is important continuously to monitor and control the chlorite concentration in such solutions.
West German Patent No. 34 37 624 discloses an apparatus with which hydrogen peroxide concentrations in liquid reaction media can be monitored and adjusted by reacting to completion with sulfur dioxide in a measuring cell a partial stream of the hydrogen peroxide-containing solution and measuring the temperature rise resulting from the heat of reaction. The temperature rise is a measure of the heat production and thus also a measure of the hydrogen peroxide concentration in the reaction medium. Similarly, the concentrations in aqueous solutions of other oxidizing agents, such as sodium chlorite, can also be measured with sulfur dioxide or other reducing agents.
The apparatus of the invention comprises a thermally insulated measuring cell, which at one end has a separate supply line for a partial stream of the oxidizing reaction medium and a separate supply line for the reacting substance, e.g., sulfur dioxide and, at the other end, a discharge line. Temperature sensors for measuring the inlet and outlet temperatures of the liquids are installed on the supply lines and on the discharge line.
This measuring cell must be connected to a partial stream line of the reaction medium and, thus, it also requires additional supply lines, metering devices, valves and/or pumps. Thus, direct connection to the delivery line of the reaction medium is desirable, said line, for example, delivering the scrubbing liquid from the bottom sump to the scrubber head of an absorption column.